This invention relates to an optical switching method and an optical switching apparatus.
Usually, the refractive index of light which relies upon the fact that incoming light to a certain substance goes out at a predetermined angle is inherent to the substance.
Various proposals have conventionally been made to use an external electric field to control the refractive index of light which is an inherent value of a substance to control the advancing direction of the outgoing light.
For example, in a "Thin film switch array" of Japanese Patent Laid-Open No. Sho 52-111739, a predetermined electric field is applied to a crystal substrate made of lithium niobate and having Ti diffused herein to lower the refractive index of the substrate to perform switching of the light path of reflected light of a predetermined wavelength. Also in a "Thin film optical switch" of Japanese Patent Laid-Open No. Sho 50-115547, a predetermined electric field is applied to a substrate made of Sr.sub.0.75 Ba.sub.0.25 Nb.sub.2 O.sub.6 to vary the refractive index of the substrate to perform switching of the light path of reflected light of a predetermined wavelength.
Another technique has been proposed wherein, if a voltage is applied to an organic material composed of an ultraviolet ray setting resin in which very fine particles of liquid crystal are dispersed and closed up, then the refractive index of light by the material varies, thereby varying the advancing direction of the outgoing light. This technique relies upon the fact that the direction in which liquid crystal molecules are arranged is varied by the voltage applied to the material.
It is also known that similar effects can be obtained where a photo-polymer having liquid crystal molecules on side chains, that is, ferroelectric liquid crystal (for example, the UCL-001 by Dai-Nippon Ink Industries, Co. Ltd.), is used.
However, in the method described above wherein a voltage is applied to an organic material composed of an ultraviolet ray setting resin in which very fine particles of liquid crystal are dispersed and closed up to vary the refractive index of light, the response time of the refractive index variation is less than 10 microseconds, that is, approximately several microseconds, and the response time of the refractive index variation where ferroelectric liquid crystal is used is approximately 10 to 40 microseconds.
The variation of the refractive index of light by a substance can be utilized for switching of a flow of a signal in an optical communication network or for information transmission in a liquid crystal display. In order to perform such switching or transmission operation rapidly, it is demanded to reduce the response time of the refractive index variation.